1) You didn't almost get arrested, campus security "arrested" you.
2) If there is no rule in the student handbook or anything posted, calmly explain that and say you want the guns returned so you can remove them from the campus. If the matter is not dropped and you are kicked out of the school, take them to court. Chances are, you'll win if you didn't violate any rules.
3) Misleading title is very misleading.